|Internet-Draft||Advertise Link No||January 2023|
|Chen, et al.||Expires 16 July 2023||[Page]|
- Network Working Group
- Intended Status:
- Standards Track
IGP Extensions for Advertising Link Numbers
This document describes OSPF and IS-IS extensions for distributing the link numbers assigned to the links originating at a node.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶
This Internet-Draft will expire on 16 July 2023.¶
Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
When the links originating at each node in a network are numbered from 1 to the number of the such links for that node, an efficient stateless multicast along an explicit P2MP path can be achieved through using the link numbers of the links on the path to represent the path.¶
This document proposes OSPF and IS-IS extensions for distributing the link numbers assigned to the links originating at a node which will support such multicast. After a controller such as PCE as a controller has the link numbers of the links originating at every node, for an explicit P2MP path, the controller can send the ingress the path represented by the link numbers of the links on the path.¶
This section describes extensions to OSPFv2 for distributing the link numbers assigned to the links of a node.¶
[RFC7684] defines the OSPFv2 Extended Link TLV to advertise the information about a link. Multiple Link TLVs for the links of a router are included in the OSPFv2 Extended Link Opaque LSA of the router. The OSPFv2 Extended Link TLV has the following format:¶
- Variable, dependent on Sub-TLVs.¶
- Link Type, Link ID and Link Data:
- They are defined in Section A.4.2 of [RFC2328].¶
- MUST be set to 0 on transmission and MUST be ignored on reception.¶
Under the OSPFv2 Extended Link TLV for a link, a Link Number Sub-TLV is defined for distributing the link number assigned to the link by the router originating the LSA. A Link Number Sub-TLV is included in the Link TLV for a link of Link Type Point-to-Point, Broadcast (i.e., link to LAN or Transit Network), or stub (i.e., link to stub network). The Link Number Sub-TLV has the following format:¶
- TBD1. (Note this is the Sub-TLV Type, not the Link Type.)¶
- Link Number:
- A 2-octet field carrying the link number assigned to the link when the Link Type of the link in the OSPFv2 Extended Link TLV containing this Sub-TLV is 1 (i.e., Point-to-Point connection to another router), 2 (i.e., connection to a Transit Network or LAN), or 3 (i.e., connection to a stub network).¶
This section describes extensions to OSPFv3 for distributing the link numbers assigned to the links of a node.¶
A Router-Link TLV defines a single router link.¶
Under the Router-Link TLV for a link, a Link Number Sub-TLV is defined. This Sub-TLV has the same format as the Link Number Sub-TLV defined above for the OSPFv2 Extended Link TLV.¶
The Router-Link TLV for a link may include a Link Number Sub-TLV for distributing the link number assigned to the link by the router originating the LSA.¶
This section describes extensions to IS-IS for distributing the link numbers assigned to the links of a node.¶
The Extended IS Reachability TLV (Type 22) defined in [RFC5305] may contain Sub-TLVs (such as those for TE (Traffic Engineering)) that apply to a link/interface to a neighbor. To encode multiple links or interfaces to neighbors, the structure inside TLV is repeated.¶
The Multi-Topology (MT) Intermediate Systems TLV (Type 222) defined in [RFC5120] may contain Sub-TLVs (such as those for TE) that apply to a link/interface. It is aligned with the Extended IS Reachability TLV (Type 22) but has an additional two bytes in front at the beginning of the TLV for MT-ID.¶
A Link Number Sub-TLV is defined and used in the Extended IS Reachability TLV (Type 22) and/or MT Intermediate Systems TLV (Type 222) to advertise the link numbers assigned to the links of a node.¶
The Link Number Sub-TLV has the following format:¶
+==============+======================+=====================+ | Value | Description | reference | +==============+======================+=====================+ | TBD1 | Link Number | This document | +--------------+----------------------+---------------------+¶
+==============+======================+=====================+ | Value | Description | reference | +==============+======================+=====================+ | TBD2 | Link Number | This document | +--------------+----------------------+---------------------+¶
Under "Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223" for IS-IS TLV Codepoints, IANA is requested to assign a codepoint for Link Number Sub-TLV as follows:¶
+============+===================+==+==+==+===+===+===+=============+ |Sub-TLV Type|Sub-TLV Name |22|23|25|141|222|223|reference | +============+===================+==+==+==+===+===+===+=============+ | TBD3 |Link Number |y |n |n | n | y | n |This document| +------------+-------------------+--+--+--+---+---+---+-------------+¶
- Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
- Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, , <https://www.rfc-editor.org/info/rfc2328>.
- Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)", RFC 5120, DOI 10.17487/RFC5120, , <https://www.rfc-editor.org/info/rfc5120>.
- Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, DOI 10.17487/RFC5226, , <https://www.rfc-editor.org/info/rfc5226>.
- Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, DOI 10.17487/RFC5305, , <https://www.rfc-editor.org/info/rfc5305>.
- Psenak, P., Gredler, H., Shakir, R., Henderickx, W., Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute Advertisement", RFC 7684, DOI 10.17487/RFC7684, , <https://www.rfc-editor.org/info/rfc7684>.
- Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
- Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and F. Baker, "OSPFv3 Link State Advertisement (LSA) Extensibility", RFC 8362, DOI 10.17487/RFC8362, , <https://www.rfc-editor.org/info/rfc8362>.
- Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250, , <https://www.rfc-editor.org/info/rfc5250>.